A novel nanocomposite was prepared by uniformly dispersing synthesized solvent-free ionic SiO2 nanofluids (NFs) into epoxy resin (EP). Tribological performance of SiO2 NFs/EP composites were investigated when rubbing against bearing steel under base oil lubrication conditions. The results demonstrate that the addition of even low-loading SiO2 NFs greatly improves the tribological performance of EP. It is disclosed that a nanostructured tribofilm grows on the steel surface when sliding against the EP nanocomposite filled with SiO2 NFs. Comprehensive analyses of tribofilms? nanostructures suggest that tribofilm growth is fed by the molecular species released from the EP nanocomposite. Formation of the load-bearing tribofilm is surmised essential for the enhanced tribological performance of the EP nanocomposite. This work paves a good formulation route for developing high-performance tribo-composites subjected to harsh lubrication conditions.